The present invention relates to cementing operations, and more particularly, to cement compositions comprising set retarder compositions and methods of using the cement compositions in surface and subterranean applications.
Hydraulic cement compositions are commonly utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of a pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that substantially supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Hydraulic cement compositions also are used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
Set retarder compositions are a common additive that may be included in cement compositions, inter alia, to delay the set time of the cement composition. Among other things, set retarder compositions may be useful not only in delaying the set time of a cement composition exposed to high subterranean temperatures, but also to extend the time the cement composition may remain pumpable after the cement composition is mixed before it is placed into the desired location. While a variety of set retarder compositions have been developed and used successfully, they have drawbacks. For instance, conventional set retarder compositions may include lignosulfonates that may provide unpredictable retardation of the cement compositions set time. Furthermore, synthetic polymers also have been used as set retarder compositions with some success. These synthetic polymers, however, may be difficult to produce, which may add undesirable expense to the cementing operation.
Set retarder compositions also have been added to cement compositions for gel strength modification. When a cement composition becomes static, it develops a property commonly referred to as “gel strength.” Gel strength is not compressive strength. Generally, there are two phases in the development of gel strength: “zero-gel time” and “transition time.” Zero-gel time, which may also be referred to as “delayed-gel time”, refers to the time period required for a cement composition to reach a gel strength of about 100 lbs per 100 ft2. During the zero-gel time, it is believed that the cement composition retains the ability to transmit hydrostatic pressure. Accordingly, the cement composition may be able to prevent the influx of formation fluids (e.g., gas) into the cement composition from the subterranean formation and associated problems. The “transition time” of a cement composition refers to the period when the cement composition has sufficient gel strength to support itself yet cannot prevent the influx of formation fluids (e.g., gases), and ending when the cement composition achieves sufficient gel strength to prevent the influx of such formation fluids. Experimentally, the transition time may be approximated by measuring the time period in which the gel strength of a cement composition progresses from about 100 lbs per 100 ft2 to about 500 lbs per 100 ft2. Additives may be added to a cement composition for gel strength modification, inter alia, to increase the zero-gel time of a cement composition and/or accelerate the transition time of a cement composition. Additives for gel strength modification include synthetic polymers, such as copolymers of 2-acrylamido-2-methylpropanesulfonic acid and N,N-dimethylacrylamide; and polymers having a tannin backbone, wherein the tannin backbone has grafted thereto a graft portion consisting of vinylamide derivatives. While these additives have been developed and used successfully, the complexity associated with their production may add undesirable expense to the cementing operation.